Intravascular arterial to venous anastomosis and tissue welding catheter

ABSTRACT

A catheter-based device tracks over a guidewire which has been placed from a first blood vessel into a second blood vessel. The distal tip of the catheter is advanced into the second vessel while a proximal member remains in the first vessel. Matching blunt tapered surfaces on each of the distal tip and the proximal member are clamped together, with adjacent walls of each vessel between them, after which a known, controlled pressure is applied between the two surfaces. Heat energy is then applied to the blunt surfaces for approximately 1-30 seconds to weld the walls of the two vessels together. After coaptation of the vessel walls, the heat is increased to then cut through the vessel walls to create a fistula of the desired size.

This application claims the benefit under 35 U.S.C. 119(e) of the filingdate of Provisional U.S. application Ser. No. 61/596,670, entitledIntravascular Arterial to Venous Anastomosis and Tissue WeldingCatheter, filed on February 8, 2012, and is also related to U.S.application Ser. No. 13/161,356, entitled Intravascular Arterial toVenous Anastomosis and Tissue Welding Cathete, filed on Jun. 15, 2011.Both of these prior applications are expressly incorporated herein byreference, in their entirety.

BACKGROUND OF THE INVENTION

In the body, various fluids are transported through conduits throughoutthe organism to perform various essential functions. Blood vessels,arteries, veins, and capillaries carry blood throughout the body,carrying nutrients and waste products to different organs and tissuesfor processing. Bile ducts carry bile from the liver to the duodenum.Ureters carry urine from the kidneys to the bladder. The intestinescarry nutrients and waste products from the mouth to the anus.

In medical practice, there is often a need to connect conduits to oneanother or to a replacement conduit to treat disease or dysfunction ofthe existing conduits. The connection created between conduits is calledan anastomosis.

In blood vessels, anastomoses are made between veins and arteries,arteries and arteries, or veins and veins. The purpose of theseconnections is to create either a high flow connection, or fistula,between an artery and a vein, or to carry blood around an obstruction ina replacement conduit, or bypass. The conduit for a bypass is a vein,artery, or prosthetic graft.

An anastomosis is created during surgery by bringing two vessels or aconduit into direct contact, and to create a leak-free blood flow pathbetween them. The vessels are joined together with suture or clips, inan open surgical procedure. The anastomosis can be end-to-end,end-to-side, or side-to-side. In blood vessels, the anastomosis iselliptical in shape and is most commonly sewn by hand with a continuoussuture. Other methods for anastomosis creation have been used includingcarbon dioxide laser, and a number of methods using various connectingprosthesis, clips, and stents. Such procedures are time consuming,clinician dependent (open to surgical error), and often result instrictures, or clotting of the vein or artery.

An arterio-venous fistula (AVF) is created by connecting an artery to avein. This type of connection is used for hemodialysis, to increaseexercise tolerance, to keep an artery or vein open, or to providereliable access for chemotherapy.

An alternative is to connect a prosthetic graft from an artery to a veinfor the same purpose of creating a high flow connection between arteryand vein. This is called an arterio-venous graft, and requires twoanastomoses. One is between artery and graft, and the second is betweengraft and vein.

A bypass is similar to an arteriovenous graft. To bypass an obstruction,two anastomoses and a conduit are required. A proximal anastomosis iscreated from a blood vessel to a conduit. The conduit extends around theobstruction, and a second distal anastomosis is created between theconduit and vessel beyond the obstruction.

As noted above, in current medical practice, it is desirable to connectarteries to veins to create a fistula for the purpose of hemodialysis.The process of hemodialysis requires the removal of blood from the bodyat a rapid rate, passing the blood through a dialysis machine, andreturning the blood to the body. The access to the blood circulation isachieved with catheters placed in large veins, prosthetic graftsattached to an artery and a vein, or a fistula where an artery isattached directly to the vein.

Fistulas for hemodialysis are required by patients with kidney failure.The fistula provides a high flow of blood that can be withdrawn from thebody into a dialysis machine to remove waste products and then returnedto the body. The blood is withdrawn through a large access needle nearthe artery and returned to the fistula through a second large returnneedle. These fistulas are typically created in the forearm, upper arm,less frequently in the thigh, and in rare cases, elsewhere in the body.It is important that the fistula be able to achieve a flow rate of 500ml per minute or greater. Dialysis fistulas have to be close to the skin(<6 mm), and large enough (>4 mm) to access with a large needle. Thefistula needs to be long enough (>6 cm) to allow adequate separation ofthe access and return needle to prevent recirculation of dialysed andnon-dialysed blood between the needles inserted in the fistula.

Fistulas are created in anesthetized patients by carefully dissecting anartery and vein from their surrounding tissue, and sewing the vesselstogether with fine suture or clips. The connection thus created is ananastomosis. It is highly desirable to be able to make the anastomosisquickly, reliably, with less dissection, and with less pain. It isimportant that the anastomosis is the correct size, is smooth, and thatthe artery and vein are not twisted.

SUMMARY OF THE INVENTION

The present disclosed invention eliminates the above described openprocedures, reduces operating time, and allows for a consistent andrepeatable fistula creation.

It is well known that heat energy, whether its source is Radio Frequency(RF), Direct Current (DC) resistance, or laser, will attach and weldtissue or vessels upon direct pressure and contact over the targetedweld area. This is often done with jaw-type, compression heat deliverydevices. It is also well known that radially expandable devices such asballoons, metal cages, and baskets are often coupled with energy in theform of RF or DC resistance, or in the case of balloons, heated saline,and used intraluminally to ablate tissue, stop bleeding, or create astricture.

The present invention uses catheter based devices that are advanced fromone vessel into an adjacent vessel (i.e. a vein into an artery), jointhe vessel walls by applying heat, and cut through the two walls,creating an anastomosis.

The inventive catheter-based devices track over a guidewire which hasbeen placed from a first vessel, such as a vein, into a second vessel,such as an artery, or more broadly between any other two vascularstructures. The distal tip of the catheter has a tapered shape whichallows the catheter to advance and dilate easily through the vesselwalls. Proximal to the distal tip, the catheter has a significantreduction in diameter, and then a blunt, oval shaped tapered surface. Asthe catheter is further advanced, the blunt proximal surface comes intocontact with the wall of the first vessel and encounters resistance, andcannot perforate through the wall into the second vessel. The distaltip, which has a matching blunt surface on its proximal end, is thenretracted, capturing the walls of the two vessels between the two bluntsurfaces. A known, controlled pressure (approximately 100 mN/mm²-400mN/mm²) is applied between the two surfaces. The pressure can becontrolled either internally in the catheter or by the handle attachedto the proximal end of the catheter. Heat energy is then applied to theblunt surfaces for approximately 1-30 seconds to weld the walls of thetwo vessels together. It is possible to apply heat energy to only onesurface as well. Heat energy can be applied through several differentmethods, including, but not limited to, RF, DC resistance, inductance,or a combination thereof The heat energy is controlled at a knowntemperature ranging from between about 150-300 C. The heat may beapplied by applying a steady energy, pulsing energy, incrementingenergy, decrementing energy, or a combination thereof.

After coaptation of the vessel walls, the heat is increased to then cutthrough the vessel walls to create a fistula of the desired size. Itshould be noted that it is also possible to apply the same heat energyto both weld the vessel walls and to cut through the vesselsimultaneously, or to cut through the vessel then weld the vessels'walls together. Alternatively, the same heat energy could be used toweld the vessel walls, followed by a non-energized, mechanically createdcut through the vessel walls.

More particularly, there is provided a device for creating anarteriovenous (AV) fistula, which comprises an elongate member, a distalmember having a tapered distal end, which is connected to the elongatemember and movable relative to the elongate member, and a first heatingmember disposed on a blunt tapered face of one of the movable distalmember and the elongate member. A second heating member is disposed on ablunt tapered face of the other one of the movable distal member and theelongate member. The heating members are adapted to cut through thetissue to create the fistula. The elongate member comprises an elongateouter tube.

A shaft connects the distal member to the elongate member, and isextendable and retractable to extend and retract the distal memberrelative to the elongate member. One of the shaft and the distal memberare fabricated of a flexible material. Preferably, the blunt taperedface on the proximal elongate member comprises a distal tapered face andthe blunt tapered face on the distal member comprises a proximal taperedface, wherein the distal tapered face and the proximal tapered face aresubstantially aligned to one another. The first heating member isdisposed on the proximal tapered face and the second heating member isdisposed on the distal tapered face. One of the first and second heatingmembers is active, and the other is passive, in some embodiments. Theactive heating member is energized, preferably by DC resistive energy.The passive heating member comprises a passive heat conductive surface.The active heating member preferably has an oval shape.

In some embodiments, the distal member is tapered and flexible. It maybe constructed to be rotatable relative to the elongate member.

Structure for retaining tissue is provided, and associated with one ofthe heating members. In illustrated embodiments, this structure maycomprise a plurality of protruding elements disposed adjacent to a faceof at least one of the heating members. At least one of the elongatemember and the distal member preferably comprises a cavity for receivingtissue retained by this structure, and this cavity is preferablydisposed within and bounded by one of the heating members.

Regarding the aligned proximal and distal tapered faces, a coating,which may be PTFE, is preferably disposed thereon to minimize tissueadhesion. Additionally, in preparation for receiving this coating, eachof the proximal and distal tapered faces are constructed to have asmooth surface finish of approximately 25-100 micro inches.

A conductive material is preferably disposed above, below, or within atleast one of the heating members, for spreading heat generated by theheating member and creating a temperature gradient emanating outwardlyfrom the heating member throughout the area of blunt tapered surface onwhich it is disposed.

In another aspect of the invention, there is disclosed a method ofcreating an AV fistula between adjacent first and second vessels, whichcomprises a step of inserting a guidewire from the first vessel into thesecond vessel, inserting a catheter comprising a proximal elongatemember and a distal member over the guidewire, so that a tapered distaltip of the distal member comes into contact with a selected anastomosissite, and advancing the distal member into the second vessel, until ablunt tapered distal face of the elongate member contacts a tissue wallof the first vessel, so that the elongate member remains in the firstvessel, thereby enlarging an aperture between the two vessels. A furtherstep involves moving the distal member and the elongate member togetherto clamp tissue surrounding the aperture between the blunt tapereddistal face of the elongate member and a corresponding blunt taperedproximal face on the distal member, and applying energy to a heatingmember on one of the distal member and the elongate member to cut andform the aperture, and to weld the edges thereof in order to create adesired fistula between the two vessels.

Preferably, during the applying energy step, a temperature of 150-300°C. is maintained at the location where the aperture is being cut. Themoving and clamping step further preferably comprises applying a known,controlled pressure between the blunt tapered distal face on theelongate member and a corresponding blunt tapered proximal face on thedistal member, wherein the known, controlled pressure is within a rangeof approximately 100 mN/mm² to 400 mN/mm².

The method may include a step of rotation the distal member during theadvancing step, for a purpose of reducing frictional resistance to thedistal member, and may also advantageously further comprise a step ofretaining cut tissue using structure associated with the heating member.This structure may include a cavity for receiving the tissue, as well asa plurality of protruding elements extending from at least one of theblunt tapered faces and surrounding the cavity.

The invention, together with additional features and advantages thereof,may best be understood by reference to the following description takenin conjunction with the accompanying illustrative drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of an embodiment of a catheter deviceconstructed in accordance with the principles of the present invention;

FIG. 2 is a view illustrating a method of access to a first blood vesselin a patient's hand, using a device of the present invention, such asthe device illustrated in FIG. 1;

FIG. 3 is a schematic view illustrating the placement of a guidewirefrom the first blood vessel into a second adjacent blood vessel, inaccordance with the present invention;

FIG. 4 is a view similar to FIG. 3, wherein the catheter is advancedover the guidewire into the first blood vessel (or vein) with the distaltip entering into the adjacent second vessel (or artery);

FIG. 5 is a view similar to FIG. 4, wherein the catheter distal tip hasbeen fully extended into the second blood vessel;

FIG. 6 is a view similar to FIG. 5, wherein the catheter distal tip hasbeen retracted to create coaptation of the first and second bloodvessels;

FIG. 7 is a view similar to FIG. 6, wherein heat energy is applied toweld and cut a communicating aperture in the coapted blood vessels;

FIG. 8 is a view illustrating in an axial orientation the coapted,welded blood vessels and communicating aperture created by the deviceand methods of the present invention after the inventive device has beenwithdrawn from the procedural site;

FIG. 9 is a schematic view in an orthogonal orientation relative to FIG.8, illustrating a detailed view of the welded blood vessels and elongatecommunicating aperture formed between the two adjacent vessels to createthe fistula;

FIG. 10 is a cross-sectional view of a handle portion of the embodimentshown in FIG. 1;

FIG. 11 is an isometric view similar to FIG. 1, illustrating analternative embodiment of the invention; and

FIG. 12 is an orthogonal view of the proximal active heat transferelement in the embodiment of FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now more particularly to the drawings, as illustrated in FIG.1, a DC resistive heat catheter 510 is shown, which comprises anelongate outer tube 512 having an outer diameter that can range from3F-12F. It may be manufactured from a variety of materials, eitherpolymeric or metallic. It comprises a central lumen 514, into which atubular structure 516, which defines its own lumen, disposed on a tip518, may slidably engage. There are separate lumens that run down theelongated core of the outer tube 512 for wiring heating elements 520,522 (proximal and distal as shown in FIG. 1 and FIG. 11 respectively),disposed on aligned blunt tapered faces 512 a and 518 a, respectively,of the respective elongate outer tube 512 and distal tip 518, and tomeasure the temperature during the coaptation and cutting processes.

In the operation of this configuration, the catheter may be poweredusing DC resistive energy to the active proximal heat transfer element520 with the distal heat transfer element 522 acting as a passive heatconductive surface to promote heat transfer through the coapted tissueinterface from the active element 520 to the passive element 522. Thesystem can also be used in an alternate configuration wherein element522 provides the active heat transfer element and element 520 providesthe passive heat conductive surface to promote heat transfer through thecoapted tissue. Both heating elements 520, 522 may be active, ifdesired. The heat transfer elements are fabricated with matching anglesto increase the surface area of coaptation and fistula size relative tothe catheter diameter. These angles can be adjusted to achieve desiredfistula sizing. The DC heat transfer elements are conductive on thefront opposing faces to maximize energy density. The DC heat transferelements 520, 522 are oval shaped and are adapted to cut an anastomosiswhich is larger than the diameter of the shaft 516. There are protrudingelements 524 adjacent to the face of proximal heat transfer element 520to promote tissue retention during welding and cutting. The entireopposing surfaces 512 a and 518 a of the proximal and distal tip heattransfer elements 520 and 522, respectively, are constructed to have asmooth surface finish of approximately 25-100 micro inches that istreated with a coating such as PTFE to minimize tissue adhesion duringor after welding and cutting.

As noted above, FIGS. 11 and 12 are noted as being illustrative of analternative embodiment. This is because, as shown in FIG. 12, it showsan alternative heating element 520 on the elongate outer tube 12.However, as illustrated, the tip 518, with heating element 522 of eachof the embodiments of FIGS. 1 and 11 may be interchangeable oridentical.

The apparatus shown and described above in connection with FIGS. 1, 10,11, and 12 will now be further described in conjunction with anexplanation of a particular method by which the system 510 may be usedto create an AV fistula. This method is illustrated more particularly inFIGS. 2-9.

To begin the inventive method of creating an AV fistula, thepractitioner selects an appropriate procedural site having each of afirst vessel 26 and a second vessel 28 in close proximity to oneanother. In currently preferred approaches, the first vessel 26comprises a vein, and the second vessel 28 comprises an artery, but theinvention is not necessarily limited to this arrangement. As illustratedin FIG. 2, one presently preferred location is the hand 30 of a patient.Then, generally employing principles of the Seldinger technique, asshown in FIG. 2, the first vessel 26 is punctured by needle 32, which isinserted therein, for the purpose of introducing an access sheath intothe site. Then, using suitable techniques, such as the techniquedescribed in Provisional U.S. application Ser. No. 61/354,903, filed onJun. 15, 2010 and U.S. application Ser. No. 13/161,182, filed on Jun.15, 2011, both applications being herein expressly incorporated byreference, in their entirety, a guidewire 34 is inserted into thepatient, from the first vessel 26 into the second vessel 28, as shown inFIG. 3.

The guidewire 34 creates an access path for catheter 510. The catheter510 is inserted into the patient by loading a proximal end of theguidewire into the lumen 516 of tip 518, which is fabricated to beflexible and tapered. Alternatively, tip 518 could be fabricated to berigid and attached to a flexible shaft 516. The catheter 510 is advancedfurther into the patient, tracking over the guidewire 34, until thetapered dilating distal tip 518 comes into contact with the selectedanastomosis site. The device 510 can be tracked over the guidewire withthe distal tip extended (as shown in FIG. 5) or retracted (as shown inFIG. 4). The distal tip is extended and further advanced into the secondvessel 28 (FIG. 5) by advancing the central tubular structure 516distally from outer tube 512, thereby dilating the opening in thevessel, so that the distal tip 518 is in the second vessel 28, and theouter tube 512 is in the first vessel 26, with its distal taperedsurface 512 a contacting the inner wall of the first vessel 26. Ifresistance is felt, tip 518 can be rotated to reduce the friction.

Alternatively, the entire system can be rotated to reduce friction. Atthis juncture, the opening fornied in the wall of vessel 26 and 28 hasrecovered back to a smaller diameter and fits tightly around the shaft516, as shown.

As noted above, the distal tip 518 of the catheter device has a taperedshape, tapering in the distal direction, which allows the catheter toadvance and dilate easily through the vessel walls. Proximal to thetapered end of the distal tip 518, at approximately point 523 (FIG. 1)the catheter has a significant reduction in diameter, because of theformation of the distal tapered end blunt face 518 a, proximal to whichis the blunt, oval shaped tapered surface 512 a of the tube 512. As thecatheter is further advanced, the blunt proximal surface 512 a comesinto contact with the wall of the first vessel 26 and encountersresistance, and cannot perforate through the wall into the second vessel28.

After the distal tip 518 is advanced into the second vessel 28, asillustrated in FIG. 6, a slight tension, or alternatively a slightpressure, is applied to the distal DC resistive heat element 522 andassociated tapered face 518 a, to seat them against the vessel 28 walland promote vessel apposition. The blunt shape of the proximal end, 512a of the distal tip 518 prevents the distal tip from inadvertentlyretracting back through the vessel wall. The proximal end of the device510, namely outer tube 512, is then advanced to close the spacingbetween the tube 512 and tip 518, until the walls of the first andsecond vessels 26 and 28 respectively, are captured between the facingblunt surfaces 512 a and 518 a, respectively, of each of the outer tube512 and distal tip 518.

A known, controlled pressure (approximately 100 mN/mm²-400 mN/mm²) isapplied between the two surfaces 512 a, 518 a. The pressure can becontrolled either internally in the catheter or by a handle 42 attachedto the proximal end of the catheter. At this juncture, with the vesselssecurely clamped (FIG. 7), heat energy is applied to the blunt surfaces512 a, 518 a for approximately 1-30 seconds to weld the walls of the twovessels together. As noted above, it is possible to apply heat energy toonly one of the two surfaces as well, with the other surface acting as apassive heat conductor. Heat energy can be applied through severaldifferent methods, including, but not limited to, RF, DC resistance,inductance, or a combination thereof The heat energy is controlled at aknown temperature ranging from between about 150-300° C. The heat may beapplied by applying a steady energy, pulsing energy, incrementingenergy, decrementing energy, or a combination thereof As the heatelements weld and cut the vessels, the heat elements will move closer toone another. When fully retracted, the system 510 is designed so thatthe two heat elements 520, 522 come into direct contact with one anotherto ensure a complete cut and capture of the vessel tissue to be removed.A variety of heat energy profiles may be used to achieve the desiredcoaptation and cutting. For example, a rapidly stepped or rampedincrease to achieve and maintain the aforementioned desired temperaturesetting of 150° C.-300° C. may be applied to maximize welding prior tocutting. Energy may be modulated based upon the impedance of the tissueor temperature feedback.

Different energy application durations, or cyclic pulses may be used tomaximize welding and cutting, while minimizing heat transfer to adjacenttissues. The distal end of outer tube 512, in the vicinity of heatelement 520, is configured to have insulating properties to minimizeheat transfer to adjacent tissues. The active heat element is an ovalshape that cuts an anastomosis larger that the diameter of the shaft516. Within the oval shape of the cutting elements, there is a cavityfor capturing the tissue that has been cut. The entire surface of theproximal and distal heat elements is configured to have a non-stickcoating, such as PTFE, to limit tissue adhesion.

After coaptation of the vessel walls, the heat is increased to then cutthrough the vessel walls to create a fistula of the desired size. Itshould be noted that it is also possible to apply the same heat energyto both weld the vessel walls and to cut through the vesselsimultaneously, or to cut through the vessel, then weld the vessel'swalls together. Alternatively, the same heat energy may be used to weldthe vessel walls, followed by a non-energized, mechanically created cutthrough the vessel walls.

Regarding the tissue welding process, as noted above, more particularly,the DC resistive energy, or other energy source, functions to fuse orweld the vessels together, creating an elongate aperture 36 (FIG. 8)through the opposing walls of each of the first and second vessels, aswell as any intervening tissue. As formed, the elongate aperture maytypically resemble a slit. However, as pressurized flow 38 begins tooccur through aperture 36, which creates a communicating aperturebetween the first and second blood vessels, the aperture widens inresponse to the pressure, taking the shape of an ellipse as it opens toform the desired fistula. The effect is illustrated in FIG. 9. The edges40 of the aperture are cauterized and welded. FIG. 9 illustrates theweld from the venous (first vessel) side. As shown, the cut areacorresponds to the shape of the heater wire. It can be of multipleshapes, such as round, oval, a slit, or a combination as shown. The areaadjacent to the cut has been welded due to the flat face of the catheterin the vein (first vessel) being larger than the cutting wire element.The heat from the cutting wire element is also preferably spread overthis area by a conductive material that can be above, below or withinthe element. This creates a temperature gradient, which is aparticularly advantageous feature of the present invention.

FIG. 10 is a cross-sectional view of the handle portion 42 of theembodiment shown in FIG. 1. This is one possible approach for actuatingthe extension and retraction of the distal tip 518 relative to theelongate outer tube 512 as discussed above, though many other suitableconfigurations may be used alternatively. A trigger 44 is slidablydisposed on the handle 42, slidable distally through a slot 46 in thedirection of arrow 48, and then retractable in the reverse direction. Aspring 50 within the handle controls pressure, and a locking mechanismfunctions to lock the trigger in the retracted state.

What is claimed is:
 1. A device for creating an arteriovenous (AV)fistula, comprising: an elongate member; a distal member having atapered distal end, connected to the elongate member and movablerelative to the elongate member; a first heating member disposed on ablunt tapered face of one of said movable distal member and saidelongate member; and a second heating member disposed on a blunt taperedface of the other one of said movable distal member and said elongatemember; wherein the heating members are adapted to cut through saidtissue to create the fistula.
 2. The device as recited in claim 1,wherein said elongate member comprises an elongate outer tube.
 3. Thedevice as recited in claim 1, and further comprising a shaft forconnecting the distal member to the elongate member, the shaft beingextendable and retractable to extend and retract said distal memberrelative to the elongate member.
 4. The device as recited in claim 3,wherein one of the shaft and the distal member are fabricated of aflexible material.
 5. The device as recited in claim 1, wherein theblunt tapered face on the proximal elongate member comprises a distaltapered face and the blunt tapered face on the distal member comprises aproximal tapered face, and further wherein said distal tapered face andsaid proximal tapered face are substantially aligned to one another. 6.The device as recited in claim 5, wherein said first heating member isdisposed on said proximal tapered face.
 7. The device as recited inclaim 6, wherein said second heating member is disposed on said distaltapered face.
 8. The device as recited in claim 1, wherein one of saidfirst and second heating members is active, and the other is passive. 9.The device as recited in claim 8, wherein the active heating member isenergized by DC resistive energy.
 10. The device as recited in claim 8,wherein the passive heating member comprises a passive heat conductivesurface.
 11. The device as recited in claim 8, wherein the activeheating member has an oval shape.
 12. The device as recited in claim 1,wherein said distal member is tapered and flexible.
 13. The device asrecited in claim 1, and further comprising structure for retainingtissue associated with one of said heating members.
 14. The device asrecited in claim 13, wherein said structure comprises a plurality ofprotruding elements disposed adjacent to a face of said one of saidheating members.
 15. The device as recited in claim 13, wherein at leastone of the elongate member and the distal member comprises a cavity forreceiving tissue retained by said structure.
 16. The device as recitedin claim 15, wherein said cavity is disposed within one of said heatingmembers.
 17. The device as recited in claim 5, wherein a coating isdisposed on each of said proximal and distal tapered faces to minimizetissue adhesion.
 18. The device as recited in claim 17, wherein saidcoating comprises PTFE.
 19. The device as recited in claim 5, whereineach of said proximal and distal tapered faces are constructed to have asmooth surface finish of approximately 25-100 micro inches.
 20. Thedevice as recited in claim 1, wherein the distal member is rotatablerelative to the elongate member.
 21. The device as recited in claim 1,and further comprising a conductive material disposed above, below, orwithin at least one of said heating members, for spreading heatgenerated by the heating member and creating a temperature gradientemanating outwardly from the heating member.
 22. A method of creating anAV fistula between adjacent first and second vessels, comprising:inserting a guidewire from the first vessel into the second vessel;inserting a catheter comprising a proximal elongate member and a distalmember over the guidewire, so that a tapered distal tip of the distalmember comes into contact with a selected anastomosis site; advancingthe distal member into the second vessel, until a blunt tapered distalface of the elongate member contacts a tissue wall of the first vessel,so that the elongate member remains in the first vessel, therebyenlarging an aperture between the two vessels; moving the distal memberand the elongate member together to clamp tissue surrounding theaperture between the blunt tapered distal face of the elongate memberand a corresponding blunt tapered proximal face on the distal member;and applying energy to a heating member on one on the distal member andthe elongate member to cut and form the aperture, and to weld the edgesthereof in order to create a desired fistula between the two vessels.23. The method as recited in claim 22, and further comprisingmaintaining a temperature of 150-300° C. at the location where theaperture is being cut, during the applying energy step.
 24. The methodas recited in claim 23, wherein the applying energy step is sustainedfor about 1-30 seconds to weld the walls of the two vessels together.25. The method as recited in claim 22, wherein the moving and clampingstep further comprises applying a known, controlled pressure between theblunt tapered distal face on the elongate member and a correspondingblunt tapered proximal face on the distal member, wherein the known,controlled pressure is within a range of approximately 100 mN/mm² to 400mN/mm².
 26. The method as recited in claim 22, and further comprising astep of rotating the distal member during the advancing step, for apurpose of reducing frictional resistance to the distal member.
 27. Themethod as recited in claim 22, and further comprising a step ofretaining cut tissue using structure associated with the heating member.28. The method as recited in claim 27, wherein said structure includes acavity.
 29. The method as recited in claim 28, wherein said structurefurther includes a plurality of protruding elements extending from atleast one of the blunt tapered faces and surrounding the cavity.